Oxidation products of 6-substituted-2, 2, 4-trialkyl dihydroquinolines as antioxidants



2,947,720 DXEDATION 'PRQDUCTS 'OF "E-SUBSTKTUTED-Zflfl- TRIALKYL DIHYDROQUINOLINES AS ANTIOX- IDANTS Frederick LiVebb, CuyahogaFalls, Ohio, assiguor to The Firestone Tire- 8; Rubber Company, Akron,- Ohio, a corporation of Ohio No Drawing. Original 'applicationfluly29; 1955; Ser. No; 525,361; Divided and this application Feb 20, 1958, Set-.NO. 716,286" a ltlClaims. c1; zen-e455 This invention relates to themse of the oxidation products. of. 6-substituted- 2,2,4=trialkyl. dihydroquinolines as antioxidants in rubber. This application is a divisionof my applicationserial No. 525,361, filed-July 29}; 1955, now U;S Patent No. 2,849,452;

The. 6-substituted-2,2,4-trialkyl 1,2 dihydroquinolines I are'commercially available. The three alkyl substituents aremethyl or-ethyl or a mixture ofthe two. The 6- substituents are alkyl, aryl, alkoxy, or -aryloxy. Thealkyl of such substituentsmay includel to 18' carbon atoms and the arylmay b'e phenyl or. phenylsubstitutedflwith I one. or more alkyl substituents of Ho 12 carbon atoms.

On oxidation, the two nitrogen groups-are united}. The oxidation compound is -ahydrazine-typematerial of}. the following formula:

in which R, R and R" are alkyl substituents of the class consisting of methyl andethyland R' is from the group consisting of alkyl, aryl, alkoxy, and aryloxy, as described.

The compounds are.made;-by oxidation of the corresponding dihydroquinolines. The dihydroquinolines in which all three alkyl substituents aremethyl, and those in which one attached to? the--2-carbon is methyl and the second and third attached to the 4-carbon is ethyl,

Patent Patented Aug. .2, 19160.

- ture. Thesolid residue weighed 14.2 g. A five-gram portion was extracted ten times with ethyl alcohol at -50 C. and three times with petroleum ether-and then air driedtogive 3- g. of a white crystalline solid melting at 121.-122. C.

Analysis.-Calcd. for. C H -N z' C, 87.07; H, 7.31; molecular weight, 497. Found: C, 86.75, 86.55; H, 7.25, 7.30.; molecular weight, 522.

EXAMPLE .II

A. solution of 20.3 g. (Oi-mole) of freshly distilled 2,2,4-trimethyl-6-ethoxy-1,2:dihydroquinoline in 400 ml. Qfpermanganate-stable acetone, was" cooled to 3: C. and.treated gradually while stirring with 9.5 g. (0.06 mole.);*of potassium permanganate. Decolorization. of the permanganate was very rapid. Later 3 g.= potassium permanganate were. added-in one-gram lots. This-also decolorizedrapidly. Themixture was filtered and the acetone evaporated at room temperature. Theresiclue was .a.dark. brown, viscous .oil. Attemptsv were made to crystallize this material by dissolving .it in petroleum ether andncooling.in.Dry-ice-alcohol. A gummy brown lmateriallseparated. The supernatantliquid waspoured off. I

From], this solution, on standing: and. partial. evaporas tion, a; crystalline solid separated; weight. 5 .0: g. r After one; washing. with alcoholand'one. recrystallization. from benzene. and alcohol, the material melted at:109.-1l0 C. Analysisr-eCalcd. for. C H O N C, 77.73; H; 8.39; molecular. weight 432.6. Found: C, 78.0.1,'78.,10;. H,- 8.20, 8.11; molecularweight- 425, 422;

Instead ofthe. foregoing starting materials, other 2,2,4= trialkyl-6-substituted4,Ldihydroquinolines-which may be used to. produce .the .f corresponding oxidation products which, in tlirn,..are suitableforzuse as. rubber. antioxidants follow-2.. 1 9 2,2,'4+trimethyl-fi-methoxy-l,2-dihydroquinoline 2,2,4-trimethyl-6r-butoxy-1,2-dihydroquinoline f 2,2;4-triethyl-6-octoxy-l;2idihydroquiuoline 2,2edimethyl-'4.-etliyl-6-undecoxy-l,2-dihydroquinoline. 2,2-dimethyl-4-ethyl-6-p1'opyl-1,Z-dihydrdquinoline.

2,2,,4-trimethyl-6-heptyl-1,2-dihydroquinoline- 2,2;4-t'riethyl-6 undecyl l,2 dihydroquinoline 2,2,4 trirhethyl 6 tolyl 1,2 dihydroquinoline a 2 2 4:t -j ethyl-6 xylyl-' 1 ,z'nmydrdquinoline 2,2,4-triinethyl 6 octyl l;2 dihydroquinoline 1 2,2,4 trimetliyl 6 octade'cyl l,2=dihydroquinoline are. commercial, as in 2,2,4-trimethyl-6-ethoxy-1,2 dihyr droquinoline and 2,2,4-trimethyl 6rphenyl 1,25dihydroquinoline, etc. When two. ditferent dihydroquinolines are oxidizedsimultaneously, the substituents in the diiferent' nuclei ofthe reaction product :will be difierent.

The following examples represent the oxidationof the quinoline compounds:

EXAMPLE I A solution" of 25 g. of 2,2,4-trimethyl-6 phenyl-1,2-dihydroquinoline in 400 ml. of permanganate-stableacetone was" treated with 11.5 g. of potassium permanganate during-a 3.5-hour period-at! C. The mixture was-fi1tered and the acetone allowed to evaporate at room-temperainner tubes, rubber-threads, foamed rubber products, and

other products from naturalrubber-ora sulfur-vulcanizable synthetic rubber homopolymer of a conjugated diene such as butadiene (e.g., polybutadiene-BR) or an alkyl derivative thereof (e.g., polyisoprene-IR), or rubber copolymer of a conjugated diene with an ethylenically unsaturated comonomer (e.g., SBR, NBR, IIR, SIR, PBR) or a mixture of any of these rubbers or any similarly vulcanizable rubber composition.

By sulfur vulcanization is meant the curing of rubber by reaction with either free sulfur or a vulcanizing agent of the sulfur-donor type. Known agents of the latter type include the various phenol polysulfides, including the alkyl derivatives thereof, the xanthogen polysulfides, the thiuram disulfides and polysulfides, various amine sulfides, including dialkylamine polysulfides and reaction products of primary amines with excess sulfur. Known vulcanization accelerators are useful in speeding up the vulcanization process and are operative herein, especially the relatively active accelerators, including the thiazole sulfenamides, e.g., cyclohexyl benzothiazole sulfenamide, thiazoline sulfenamides, thiocarbamyl sulfenamides, mercaptothiazoles, mercaptothiazolines, thiazolyl monoand disulfides, the dithiocarbamates, the thiuram sulfides, xanthogen sulfides, 'metallic salts of mercaptothiazoles, mercaptothiazolines and dithiocarbamic acids. One or more accelerator'activator is often used with any of the accelerators mentioned, and such activators include the various derivatives of guanidine known in the art, amine salts or organic and inorganic acids, various amines themselves, alkaline salts such as sodium acetate and the like, as'well as other activators known to the art.

Additionally, two or more accelerators or accelerator combinations are sometimes desirable in a single rubber compound. Many of the accelerators mentioned above are suitable in latex formulations, especially such common accelerators as piperidinium pentamethylene dithi carbamate, zinc butyl xanthate, zinc ethyl xanthate, zinc salt of mercaptobenzolthiazlole, zinc dimethyl dithiocarbamate, zinc dibutyl dithiocarbamate. Although vulcanization is usually accomplished by heating a vulcanizable rubbertcomposition at a temperature in the range of 240 to 400 F. for a time ranging from several hours to a few seconds, vulcanization does take place at lower temperatures, such as ordinary room temperature, It is quite common to vulcanize a latex film containing an ultra-accelerator by allowing the film to remain at room temperature for several hours or a few days. V

The antioxidants of Examples I and II were compounded with rubber according to the following formula for a tread stock:

The various samples were cured 40 minutes at 280 F. The test properties of the cured samples are recorded in the following table, and these properties are compared with a blank similarly compounded but including no antioxidant. In the tables, modulus, tensile strength, and elongation are recorded in pounds per square inch. Oxygen absorption by the various samples was determined as described in the article by IR. Shelton and Hugh Winn in Industrial and Engineering Chemistry, volume 38, page 71 (1948). By plotting the milliliters of oxygen absorbed per gram of rubber polymer, against the hours required for the absorption, and determining the slope of the straight-line portion of each curve which refers to the constant rate of oxygen absorptiomthe rates of absorption were obtained and are given in the tables.

Table 1 Formulation:

Masterbatch 164 164 Blank Example I- 1 Normal Properties:

Modulus (300%) 1, 800 Modulus (400%) 2, 800 Tensile 3, 975 Elon ation 500 490' Properties After Aging 2 Days (Air Oven) at 212 F.:

Modulus (300%) 2, 025 2, 125 Tensile 2, 025 2, 425 Tensile retained, percent 55 61 Elon ation 315 340 Oxygen Absorption, 0.:

Hours for absorption, 10 ml./g. rubber 19. 5 30 Total hours in absorption apparatus 32 55 Total oxygen absorbed, mL/g. rubber 15. 8 20. 2 Rate of oxygen absorption m1.lhr./g 0.380 0.252 Properties Alter Oxygen Absorption:

Modulus (300%) Tensile 575 1, 050 Elongation 180 250 A sample was prepared according to the same tread stock formula with one part of the oxidation product of Example H, and compared with a typical blank. The results are recorded below: 1

Table 2 Formulation:

Masterbateh 164 164 Blank (typical) Example 2- 1 Normal Properties:

odulus 300% 1, 900 2, 025 Modulus 400% 2, 825 3, 200

' Tensi 3, 990 3, 775 Elon ation 500 465 Oxygen Absorption 90 0.:

- Hrs. for absorption, 10 mlJg. rubber. 19. 5 27 Hrs. for absorption, 20 mL/g. rubber. 44 Total hrs. in absorption apparatus" 32 45 Total oxygen absorbed/g. rubber 15. 8 22. 6 Rate of oxygen absorption, m1./hr./g 0.380 0. 246

Properties After Oxygen Absorption:

; Tensile 575 1, 225 Elon ation 180 240 The results of the foregoing tests, as reported in both tables, show the compounds of this invention have a decided stabilizing elfect, and produce improved vulcanizates.

The antioxidants are used in any small amount, as for example 0.1 to 10 parts per parts of rubber.

The invention is defined by the claims which follow.

What I claim is:

l1. Vulcanized rubber which contains a stabilizing amount of a stabilizer having the formula in which R, R' and R" are alkyl substituents of the class consisting of methyl and ethyl and R' is from the group consisting of alkyl, aryl, alkoxy and 'aryloxy; the alkyl groups of the foregoing alkyl and alkoxy substituents each containing 1 to 18 carbon atoms, and the aryl groups of the foregoing substituents being from the class consisting of phenyl and phenyl substituted with at least one substituent of l to -12 carbon atoms; the rubber being of the class consisting of sulfur-vulcanizable natural and synthetic rubbers which are from the class consisting of homopolymers of conjugated dienes and copolymers of conjugated dienes and an ethylenically' unsaturated .comonomer.

2. Vulcanized rubber of claim 1 which contains a stabilizing amount of a compound of the given formula in which R, R and R" alkyl groups are methyl.

3. Vulcanized rubber of claim 1 which contains a stabilizing amount of the compound of the given formula in which R, R and R alkyl groups are methyl and the two R' groups are phenyl.

4. Vulcanized rubber or claim 1 which contains a stabilizing amount of the compound of the given formula in which R, R and R" alkyl groups are methyl and the two R groups are ethoxy.

5. Vulcanized rubber of claim 1 which contains a stabilizing amount of a compound of the given formula. in which R, R and R" alkyl groups are methyl and the two R' groups are alkyl groups each containing 1 to 18, inclusive, carbon atoms.

6. The process of vulcanizing rubber which comprises sulfur-vulcanizing the rubber in the presence of a stabilizing amount of a compound having the formula in which R, R and R of the foregoing substituents being from the class oon sisting of phenyl and phenyl substituted with at least one substituent of 1 to 12 carbon atoms; the rubber being from the class consisting of sulfur-vulcanizable natural and synthetic rubbers which are from the class consisting of homo-polymers of conjugated dienes and copolymers of a conjugated diene and an ethylenically unsaturated comonomer.

7. The process of vulcanizing rubber according to claim 6 which comprises suliur-vulcanizing the rubber admixed with a stabilizing amount of a compound of the given formula in which the R, R and R" groups are methyl.

8. The process of vulcanizing rubber according to claim 6 which comprises sulfur-vulcanizing the rubber admixed with a stabilizing amount of the compound of the given formula in which R, R' and R" alkyl groups are methyl and both R groups are phenyl.

9. The process of vulcanizing rubber according to claim 6 which comprises sulfur-vulcanizin-g the rubber admixed with a stabilizing amount of the compound of. the given formula in which R, R and R" alkyl groups are methyl and both R'" groups are ethoxy.

10. The process of vulcanizing rubber according to claim 6 which comprises sulfur-vulcanizing the rubber admixed with a stabilizing amount of the compound of the given formula in which R, R and R" alkyl groups are methyl and both R' groups are alkyl groups each containing 1 to 18, inclusive, carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS 2,500,229 Arnold et al Mar. 14, 1950 2,713,047 Beaver et a1. July 12, 1955 FOREIGN PATENTS 468,787 Great Britain r July 12, 1937 

1. VULCANIZED RUBBER WHICH CONTAINS A STABILIZING AMOUNT OF A STABILIZER HAVING THE FORMULA 